Compared to Professionals, High School Baseball Pitchers Throw with Different Rotational Kinematics

Luera MJ, Dowling B, Magrini MA, Muddle TW, Colquhoun RJ, Jenkins ND. Role of rotational kinematics in minimizing elbow varus torques for professional versus high school pitchers. Orthop J Sport Med. 2018;6(3):1-8. doi:10.1177/2325967118760780

Background

The ulnar collateral ligament (UCL) is the primary structure responsible for supplying varus torque in response to high valgus stress generated during the throwing motion.  UCL injury rates are on the rise and this increase is most alarming in the 15 to 19-year-old age range.  Analysis of pitching kinematics in this age group, in comparison to older players, can help identify biomechanical differences that may lead to improved performance and reduced injury risk.

Purpose

To examine pitch velocity and the kinetic and kinematic differences between high school and professional pitchers in order to identify potential associations with increased risk of injury in youth pitchers.

Study Population

  • Thirty-seven (n=37) high school baseball pitchers without injury in the last 6 months
  • Forty (n=40) professional minor league (Low-A, High-A, AA, and AAA) pitchers without injury in the last 6 months

Methods

Research participants completed a single session of pitching at maximum effort assessed with a motion analysis system.  Pitch velocity (PV), absolute and normalized elbow varus torque (EVTA and EVTN, respectively) was analyzed during arm cocking and at maximum shoulder external rotation (MER).  Eight other upper extremity torques or forces were analyzed along with rotational kinematics of the hips, pelvis and trunk.

Key Results

  • EVTA was greater in professional versus high school pitchers during arm cocking and at MER.
  • EVTN was similar during arm cocking but greater in high school versus professional pitchers at MER.
  • In professional pitchers
    • PV was not related to EVTA during arm cocking or at MER (r = 0.01-0.05).
    • EVTA during arm cocking and at MER was inversely related to upper trunk rotation at hand separation and foot contact and pelvis rotation at maximum elbow extension (r = –0.30 to –0.33).
  • In high school pitchers
    • PV was related to EVTA during arm cocking and MER (r = 0.76 to 0.77).
    • PV and EVTA during arm cocking and at MER were related to multiple elbow and shoulder torques and forces (r = 0.424 to 0.991).
    • EVTA was not related to upper trunk or pelvis rotation throughout the throwing motion (r = – 0.16 to 0.15).
  • For upper trunk lateral flexion, upper trunk flexion, pelvic tilt, and lead hip rotation there were no phase x group interactions.
  • Combined across all phases of throwing, upper trunk rotation was greater in professional pitchers.
  • Pelvis rotation and back hip rotation was significantly greater in professional versus high school pitchers.

Study Limitations

  • Selection bias from small samples of high school and minor league professional pitchers.
  • No cause-and-effect relationships can be established from this study design.

Closing Thoughts & Practical Implications

Not surprisingly, professional pitchers throw at higher velocities and with greater absolute elbow varus torque.  However, when normalized by body mass, high school pitchers demonstrate greater elbow varus torque at maximal external rotation.  Professional pitchers throw with greater hip, pelvis, and upper trunk rotation compared to high school pitchers.  The ability to rotate through the pelvis and trunk may allow professional pitchers to generate greater fastball velocities without increasing elbow varus torque.

Velocity is associated with absolute elbow varus torque in high school but not professional pitchers.   High school pitchers without the same rotational capabilities as professionals may seek to generate increased velocity through methods that increase torque at the shoulder and elbow.   Transfer of forces up the kinetic chain during pitching via hip, pelvis, and trunk rotation may play an important role in limiting the torque imposed on the UCL.  Professional pitchers are better able to accomplish this while generating greater ball velocities. Improving rotational kinematics in youth pitchers may increase velocity and help protect the pitcher from upper extremity injury.

Pitchers with exceptional hip, pelvis, and trunk capabilities may be naturally selected to play at the highest of levels.  It is also plausible that optimal training and conditioning targeting rotational mobility, strength, and power can increase a high school athlete’s chance of reaching higher levels of competition.  Rehabilitation and strength and conditioning specialists can consider the findings of this study when developing programs for youth pitchers.  Optimizing a youth pitcher’s ability to rotate through the hips, pelvis, and trunk may have profound effects on performance and decreasing injury risk.

 

 

 

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